Zeolites are crystalline oxides with micropores (e.g., pores with sizes in the range of 0.3 to 1.2 nm) and compositions (e.g., Si, Al, Ti, P, Ge, Zn content) that may be fine-tuned for many important applications such as catalysis, adsorption, and ion exchange.
Apart from the use of zeolites in a powder form, thin films and membranes of zeolites are of particular commercial interest as energy-efficient alternatives to current separation and purification processes like distillation, crystallization, and others.
Zeolite molecular sieve membranes can in principle be used in a wide range of operating conditions including high temperatures, high pressures, and in reactive environments, while they can be regenerated for fowling and contamination by aggressive treatments like high temperature calcination under, for example, vacuum or in oxygen or air atmospheres.
Due to these superior properties of zeolite membranes, there have been a range of zeolites prepared in the form of membranes, such as zeolite A, faujasite (X and Y forms), mordenite, ferrierite, MEL, zeolite P, chabazite, SAPO-34, DDR, MFI, i.e., Zeolite Socony Mobil (ZSM)-5.
Thin films of zeolites are technologically valuable for such applications as gas or liquid separations, chemical sensors, membrane reactors, and optoelectronic devices. Due to their well-defined rigid pores in the molecular dimensions and high thermal and chemical stability, zeolite thin films are of particular interests as high resolution selective membranes.
Despite the promise of zeolite membranes as a class of high-performance material, there exist few reports on the practical applications of such membranes. In fact, there is only one commercial application of zeolite membranes so far, zeolite A membranes for water-alcohol separation. To find more commercial applications of zeolite membranes, there are a number of challenges that are yet to be addressed. Some of the challenges include: (1) synthesis of membranes with high permeability and selectivity, which require these membranes to possess small effective thicknesses, and low defect density; (2) membrane fabrication that is cost-effective, reproducible and amenable to scale-up. There is continuing interest to improve the membrane preparation methods and the produced membrane performance.